1. Field of the Invention
This invention relates to particles of activated substance coated with an inactive protective layer and to a method for the manufacture thereof.
2. Description of the Prior Art
Generally when a substance possessing an active group is put to use in a solid state as in the form of particles, for example, there is a possibility that the active group present on the surface of such solid particles will produce an undesirable side effect. When dialdehyde starch having the aldehyde group as its active group is used for the removal of urea, ammonia and lower amines from the blood or body fluid, for example, the active aldehyde group distributed on the surface of the starch particles comes into contact with the blood or body fluid and readily reacts with many effective components contained in such fluid. When the dialdehyde starch is orally administered in an effort to eliminate urea, ammonia, etc. from within the intestinal tract, the active aldehyde group present on the surface of the starch particles readily reacts not only with the amino groups of the protein molecules forming the inner walls of the oral cavity, the gastric tract and other digestive organs but also with the amino groups resulting from the digestive decomposition of food. These side reactions are hardly negligible.
With a view to overcoming such drawbacks, particulate solid substances (such as oxidized starch) simply coated physically with microcapsules of ethyl cellulose have been proposed as described in the article "Removal of Uremic Waste Metabolites from the Intestinal Tract by Encapsulated Carbon and Oxidized Starch" of the Transaction of American Society Artif. Int. Organs, 17, 229.about.(1971), written by R. E. Sparks, N. S. Mason, P. M. Meier, M. H. Litt, and O. Lindan. These particles, however, have the disadvantage that the microcapsules applied as the coat thereto are incomplete and, therefore, allow the active aldehyde group distributed on the surface of the particles to be partially exposed through breaks in the coat and left to give rise to undesirable side reaction.